Means for limiting the residual level during superimposed over-voltage conditions in a surge diverter

ABSTRACT

In a surge diverter, in order to limit the residual level during superimposed over-voltage conditions, a plurality of spark gap stacks with associated non-linear resistors are provided with a shunt spark gap shunting at least one spark gap stack with the associated non-linear resistor. A shunt impedance is provided shunting at least one spark gap stack which is shunted by the shunt spark gap. The surge diverter includes a sufficient number of shunt gaps to prevent the total voltage over the diverter upon super-imposed over-voltage conditions from exceeding the protection level of the diverter.

ilnited States Patent 1191 Schei 1 May 15, 1973 [54] MEANS FOR LIMITINGTHE [56] References Cited RESIDUAL LEVEL DURING UNITED STATES PATENTSSUPERIMPOSED OVER-VOLTAGE 3,489,949 1/1970 Carpenter ..3I7/69 XCONDITIONS IN A SURGE DIVERTER 3,673,459 6/1972 Carpenter ..3l5/363,348,100 10/1967 Kres e l ..3l7/70 [75] Invent Asle sch", Ludvlka,Sweden 3,414,759 12/1968 Conn ell et a1. ....317 70 x Assignee: AumannaSvenska Elektriska 3,413,524 11/1968 Tram ..3]7/69 tlebolaget VasterasSweden Primary ExaminerC. L. Albritton [22] Filed: Apr. 28, 1972Attorney-Jennings Bailey, Jr. [21] App]. No.: 248,601 ABSTRACT In asurge diverter, in order to limit the residual level [30] ForeignApplication Priority Data during superimposed over-voltage conditions, aplurality of spark gap stacks with associated non-linear May 3, 1971Sweden ..5673/71 resistors are provided with a Shunt spark p shunting atleast one spark gap stack with the associated non- CL 317/70, linearresistor. A shunt impedance is provided shunt- 338/2] ing at least onespark gap stack which is shunted by [51] Int. Cl. ..H02h l/00 the shuntspark gap. The surge diverter includes a suf- [58] Field of Search..338/2l, 13, 20; ficient number of shunt gaps to prevent the totalvoltage over the diverter upon super-imposed over-voltage conditionsfrom exceeding the protection level of the diverter.

4 Claims, 7 Drawing Figures I MEANS FOR LIMITING THE RESIDUAL LEVELDURING SUPERIMPOSED OVER-VOLTAGE CONDITIONS IN A SURGE DIVERTERBACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to a means for limiting the residual level during super-imposedover-voltage conditions in a surge diverter.

2. The Prior Art A surge diverter in an electric power line may undercertain conditions during the extinguishing interval of the diverter besubjected to superimposed overvoltages or over-voltages superimposed onthe operating voltage. Such conditions are most likely to appear inequipment for high voltage direct current and may occur when differentdiverters in the equipment ignite at different moments. An example ofthis is when a diverter for a converter-rectifier sparks-over while aphase-earth diverter discharges a connection overvoltage from the ACside. The phase-earth diverter is then connected to the DC line over thediverter of the converter-rectifier, thus causing a current increase inthe phase-earth diverter. At the moment when the diverter over theconverter-rectifier is ignited, the phaseearth diverter may very welloperate with arcs extended by a magnetic field and under such conditionsnormal diverters do not give sufficient protection.

SUMMARY OF THE INVENTION The present invention relates to a means forsurge diverters, preferably in equipment for high voltage directcurrent, to limit the residual level during superimposed over-voltageconditions.

According to the invention, in a surge diverter, in order to limit theresidual level during super-imposed over-voltage conditions, a pluralityof spark gap stacks with associated non-linear resistors are providedwith a shunt spark gap shunting at least one spark gap stack with theassociated nonlinear resistor. A shunt impedance is provided shunting atleast one spark gap stack which is shunted by the shunt spark gap. Thesurge diverter includes a sufficient number of shunt gaps to prevent thetotal voltage over the diverter upon superimposed over-voltageconditions from exceeding the protection level of the diverter.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings FIGS. 1,2 and 3 show three different embodiments of the invention and FIG. 4shows the total discharge current through the surge diverter as afunction of the time;

FIGS. 5 and 6 show the voltage over the non-linear valve-resistors andthe voltage over the spark gap in a phase-earth diverter, for example;

FIG. 7 shows the total voltage over the diverter as a function of thetime. The four latter figures show the conditions during super-imposedover-voltage conditrons.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A surge diverter according toFIGS. 1, 2, and 3 comprises a number of spark gap stacks 1 alternatingwith non-linear valve-resistors 2. Parallel therewith is a control chainwith control impedances 3. The figures only show part of a diverter.

In order for the diverter to be able to protect even under theconditions mentioned during super-imposed over-voltages, it is nowproposed that a number of gapplus-block units are shunted with an extraspark gap, shunt gap,4. FIG. 1 shows two gap stacks and a resistor beingshunted, whereas FIG. 2 shows the case in which the shunt gap bridges agap stack and a resistor. In FIG. 3 the valve-resistor 2 is a part ofthe control chain. Other combinations are of course also possible. Inview of the ability of the diverter to limit the ensuing current it isadvisable to use gaps with magnetic blowing for the shunt gaps as well.In the examples shown in FIGS. 1 and 3 it is preferable to shunt one ofthe spark gap stacks l shunted by the spark gap 4, with a shuntimpedanceS. The spark-over voltage of the shunt gap 4 is chosen so highthat it does not fire during normal over-voltages but only when suchsuperimposed overvoltages occur as might jeopardize the protectivecapacity of the diverter. The number of shunts necessary for a certaindiverter may vary from time to time and can be determined so that thediverter can ensure the necessary protection level.

FIG. 4 shows the current as a function of the time in a phase-earthdiverter,for example. At the time t 0 the phase-earth divertersparks-over and the current increases to its maximum value, after whichit decreases in the normal manner. At the time 2,, however, aconverter-rectifier diverter sparks-over so that the DC line isconnected to earth over the two diverters in series, the currentincreasing almost instantaneously to a high value and then decreasing.

FIG. 5 shows the corresponding sequence for the voltage U,, over theresistance block in the first sparked-over phase-earth diverter. At thetime t, a voltage peak appears. In the same way, FIG. 6 shows thevoltage over the gap stacks. From a low value immediately after the gapshave sparked-over the gap voltage increases as the arcs are extendedbecause of the magnetic blowing. However, here also a strong voltagepeak occurs at the time t when the second diverter sparks-over.

FIG. 7 shows the voltage U,, over the phase-earth diverter, this voltagebeing U,, U

In the last three figures the protection level U of the diverter isindicated by a broken line and from FIG. 7 it is clear that the totalvoltage over the diverter exceeds its protection level, so that thediverter is not capable of protecting the equipment.

If according to the invention some of the spark gaps and valve-resistorblocks are shunted with extra gaps, this means that part of the voltagepeak occuring at the time t in FIGS. 5 and 6 can be removed. The numberof shunt gaps is chosen so that the voltage peak at t shown in FIG. 7 iskept under the line U,,.

I claim:

1. In a surge diverter, means to limit the residual level duringsuperimposed over-voltage conditions, said means comprising a pluralityof spark gap stacks (1) with associated serially connected non-linearresistors, and a shunt spark gap shunting at least one spark gap stack(1) with the associated non-linear resistor (2).

2. In a device according to claim 1, said shunt spark gap shunting twospark gap stacks (1) having a nonlinear resistor (2) connectedtherebetween.

3,733,520 3 4 3. In a device according to claim 1, having a shunt venttotal voltage (U over the diverter upon superimpedance (5) shunting atleast one Spark gap Smck imposed over-voltage conditions from exceedingthe (1) which is shunted by the shunt spark gap.

4. In a device according to claim 1, the surge diverter includes asufficient number of shunt gaps (4) to pre- 5 protection level (U,,) ofthe diverter.

1. In a surge diverter, means to limit the residual level duringsuperimposed over-voltage conditions, said means comprising a pluralityof spark gap stacks (1) with associated serially connected non-linearresistors, and a shunt spark gap shunting at least one spark gap stack(1) with the associated non-linear resistor (2).
 2. In a deviceaccording to claim 1, said shunt spark gap shunting two spark gap stacks(1) having a non-linear resistor (2) connected therebetween.
 3. In adevice according to claim 1, having a shunt impedance (5) shunting atleast one spark gap stack (1) which is shunted by the shunt spark gap.4. In a device according to claim 1, the surge diverter includes asufficient number of shunt gaps (4) to prevent total voltage (Ua) overthe diverter upon super-imposed over-voltage conditions from exceedingthe prOtection level (Un) of the diverter.